A wireless communication network may support Packet Switched (PS) services and/or Circuit Switched (CS) services. Network equipment for a wireless communication network can be divided into access network equipment and core network equipment. An access network and a core network are connected. A single core network can be supported by multiple different access networks. An example of a core network that supports PS services is the Evolved Packet Core (EPC). An example of a core network that supports CS services is the Network Switching Subsystem (NSS) or Global System for Mobile Communications (GSM) core network.
Examples of access networks are: GSM EDGE Radio Access Network (GERAN); Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access Network (UTRAN); Evolved UTRAN (E-UTRAN); Wireless Local Area Network (WLAN) based access networks, including Institute of Electrical and Electronics Engineers (IEEE) 802.11 networks. GERAN, UTRAN, E-UTRAN are examples of 3rd Generation Partnership Project (3GPP) access networks. WLAN-based access networks (including IEEE 802.11) and 1X CDMA are examples of non-3GPP access networks. Some, but not all, access networks support CS services. Some, but not all, access networks support PS services. E-UTRAN is an example of a 3GPP access network that supports PS services, such as Internet Protocol (IP) Multimedia core network Subsystem (IMS) voice. WLAN networks are examples of non-3GPP access networks that may provide PS services, such as Voice over IP (VoIP) services. GERAN, UTRAN, and 1XCDMA are examples of 3GPP access networks that support CS services. The E-UTRAN and the EPC make up the Evolved Packet System (EPS). The EPS is an evolution of the 3G UMTS characterized by higher-data-rate, lower-latency, packet optimized system that supports multiple Radio Access Technologies (RATs).
The wireless communication network may support one or more communication services for a mobile communication device. Examples of communication services are voice service, text message service, data service, and video service. Examples of these communication services as implemented in a CS domain and delivered to a user by the mobile device are CS voice service, Short Message Service (SMS) and Unstructured Supplementary Service Data (USSD). A communication service may also be supported or realized using a PS service. For example, a same or similar functionality of a CS service (such as a voice service) may be supported using a PS service (such as IMS PS voice or VoIP). Thus, for a given type of communication service (e.g. voice, text, data, etc.) the service may be supported using a “PS-version” or a “CS-version” of the service. IMS PS services may be provided by a 3GPP network. VoIP services may be provided by a WLAN network. IMS and VoIP may utilize the Session Initiation Protocol (SIP).
The mobile device collaborates with the network equipment to support PS and CS services. The mobile device may, for example, utilize SIP components forming part of the mobile device to support PS services provided by the network. A mobile device terminating the SIP protocol can receive and transmit SIP messages configured to support the PS service. Certain SIP request messages request creation of a dialog. For example, a SIP INVITE message is a request for a dialog. When a dialog is created, media may be exchanged between both ends of the dialog. A SIP user agent (UA) terminates a dialog. Voice is an example of media. A SIP dialog that includes voice media can be thought of as a voice call.